In this paper, a new single crystal (SC) superalloy YH61 is proposed to solve the problem of grain defects which are present in single crystal buckets or vanes of industrial gas turbines. First, the effects of solution heat treatment on various properties of the SC with and without grain defects were evaluated. Increasing the solution-heat-treated area was found to have a positive effect on the strength of a defect-free SC but harmful for the strength of a grain boundary and growth of recrystallizatior~ The solution heat treatment condition for YH61 was determined after considering properties of both the defect-free SC and the SC with grain defects. Secondly, the effects of grain boundary misotientation angle (a) on the mechanical properties of grain boundaries were examined at several temperatures. No significant decrease in strength was found with increasing a at temperatures below about 8Oo"C, although the fall-off of strength was observed with increasing a at temperatures above about this temperature. Even when a significant decrease in strength was not observed, unexpected deformation behavior was found with increasing a because the S&mid factor for the slip system was also increased with increasing a. In a strain-controlled LCF test, another type of deformation was observed for higher a values. This deformation caused significant fall-off of life as a function of a. From the results of long term creep-rupture tests, YH61 was found to show similar creep-rupture strength to a second generation single crystal superalloy under certain conditions although YH61 contains higher levels of grahr boundary strengthening elements.
Ba2YCu3O7-δ tapes were fabricated by cold rolling. The critical current density J
c apparently depended on the thickness of the tape and increased markedly with decreasing tape thickness. The maximum J
c of 3330 A/cm2 at 77 K in a zero magnetic field was achieved in an Ag-sheathed BYCO tape, 0.06 mm in thickness. The presence of a 20 mT magnetic field reduced the J
c value by 1/100.
Ag-sheathed tapes using tetragonal phase of YBa2Cu3O
x
were fabricated by cold rolling. Neutron diffraction study was undertaken to investigate the orientation of YBCO grains in the Ag-sheathed tape. It was clearly observed that the c-plane of crystal was aligned parallel to the cold rolling surface with a standard deviation of 26.7 degree. The preferred orientation was enhanced by using the tetragonal phase.
In order to study possibilities of application of rapid solidification ribbons to an insert metal for solid phase diffusion welding of Ni-base supearlloy, welding was carried out by changing the welding pressure, time, and temperature using Ni-base superalloy ribbons (IN738LC, TMP-3, Ren6 80, and Ni-Al-X three compositional alloys) produced by twin-roll rapid solidification process. The ribbon has almost similar composition to the base metal (Rene 80) and superplastic potential, then it needs relatively small flow stress on deformation. In this report, the influence of ribbon usage as an insert metal and carbon content in the ribbon on the joint strength were studied. The results are as follows,(1) The joint strength increases by using the ribbon,for an insert metal compared to that without ribbons.(2) Carbide and oxide are formed on the welded interface during welding, resulting in decrease in weld ing strength.(3) The joint strength is increased and fractured position changes from the welded interface to the base metal, as the carbon content in the ribbon is decreased.
Synopsis:Particle size distributions, microstructures and residual gas contents of high speed steel powders, atomized by spraying water or argon gas have been investigated. The particle size distributions and the microstructures of the water-atomized powders are finer than those of the argon-atomized powders. Oxygen contents of the water-atomized powders are higher, but can be easily reduced by sintering in a vacuum furnace.In the argon-atomized powders, argon included in the powders are observed.Sintered and hot-forged high speed steels of low oxygen contents have high transverse rupture strength and notch-toughness, because of their uniformly fine microstructures.Retained austenite is decreased and grinding is also relatively easy in the sintered and hot-forged high speed steels of fine microstructures.
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